[imp] IDN support for horde / imp auth login.

[info at interpost.biz]

  Hello, running debian stretch repo horde (5.1.17) webmail edition  
with dovecot and postfix, apache 2.4 and mariadb 10.3, php 7.2:   we  
cannot login to horde (authenticating over ssl to imp) with the IDN,  
but must use punycode.  I have configured dovecot to accept the  
accented characters contained in the mail domains, and this doesn't  
help.  Roundcube allows us to do login using the IDN  (i.e.  
info at cuvé.com) , so I don't think the error is with dovecot.  

Does horde authenticating through imp support IDN's fully?  If not, is  
there a specific sanitizer or validator that I could change in the imp  
auth process to allow accented characters? Or a library to be used. We  
aren't using mbstring to do any conversion as this is very problematic  
with other applications, and since roundcube works natively, it  
shouldn't be necessary.

Is anyone successfully using horde + imp with IDN logins?  How?

Thanks,
 

  Ed